Photoelectric conversion device, imaging system, and moving body

ABSTRACT

Provided is a photoelectric conversion device including a first holding portion that holds charges transferred from at least one of a first photoelectric conversion unit, a second photoelectric conversion unit, and a third photoelectric conversion unit, the first photoelectric conversion unit and the second photoelectric conversion unit are arranged adjacent to each other along a first direction, the first photoelectric conversion unit and the third photoelectric conversion unit are arranged adjacent to each other along a second direction, which is different from the first direction, and the first holding portion is arranged at a position at least partially overlapping a straight line connecting the optical center of the second photoelectric conversion unit to the optical center of the third photoelectric conversion unit.

BACKGROUND Technical Field

One disclosed aspect of the embodiments relates to a photoelectricconversion device having high sensitivity, an imaging system, and amoving body.

Description of the Related Art

In recent years, CMOS image sensors suitable for low consumption powerand high-speed reading have been widely used for photoelectricconversion devices used in digital still cameras, digital video camera,or the like. In CMOS image sensors, those having a function of globalelectronic shutter to match exposure timings of a plurality of pixelshave been proposed. Japanese Patent Application Laid-Open No.2009-296574 discloses a photoelectric conversion device in which holdingportions that hold charges generated by photoelectric conversion for apredetermined period are provided in order to implement the function ofglobal electronic shutter.

To realize higher sensitivity, driving to add charges of a plurality ofpixel rows and add charges of a plurality of pixel columns of aphotoelectric conversion device may be performed. Japanese PatentApplication Laid-Open No. 2009-296574 does not disclose a specificlayout that may be applied to a photoelectric conversion device adaptedto such addition of charges. Therefore, there is room to improveperformance of a photoelectric conversion device by optimizing layoutdesign.

SUMMARY

The present disclosure has been made in view of the problem describedabove and intends to provide a high-performance photoelectric conversiondevice, an imaging system, and a moving body.

According to an aspect of the present disclosure, a photoelectricconversion device includes a substrate; a first photoelectric conversionunit, a second photoelectric conversion unit, a third photoelectricconversion unit, a first holding portion, a first transfer unit, asecond transfer unit, a third transfer unit, and a first amplifier unit.The first, second, and third photoelectric conversion units are arrangedon the substrate and each configured to generate charges in accordancewith incident light. The first holding portion is arranged on thesubstrate and configured to hold charges transferred from at least oneof the first photoelectric conversion unit, the second photoelectricconversion unit, and the third photoelectric conversion unit. The firsttransfer unit is arranged on the substrate and configured to transfercharges from the first photoelectric conversion unit to the firstholding portion. The second transfer unit is arranged on the substrateand configured to transfer charges from the second photoelectricconversion unit to the first holding portion. The third transfer unit isarranged on the substrate and configured to transfer charges from thethird photoelectric conversion unit to the first holding portion. Thefirst amplifier unit includes an input node configured to receivecharges transferred from the first holding portion. The firstphotoelectric conversion unit and the second photoelectric conversionunit are arranged adjacent to each other along a first direction in planview with respect to the substrate. The first photoelectric conversionunit and the third photoelectric conversion unit are arranged adjacentto each other along a second direction, which is different from thefirst direction, in the plan view. The first holding portion is arrangedat a position at least partially overlapping a straight line connectingan optical center of the second photoelectric conversion unit to anoptical center of the third photoelectric conversion unit in the planview.

According to another aspect of the present disclosure, a photoelectricconversion device includes a substrate, a first photoelectric conversionunit, a second photoelectric conversion unit, a third photoelectricconversion unit, a fourth photoelectric conversion unit, a first holdingportion, a first transfer unit, a second transfer unit, a third transferunit, a fourth transfer unit, and a first amplifier unit. The first,second, third, and fourth photoelectric conversion units are arranged onthe substrate and each configured to generate charges in accordance withincident light. The first holding portion is arranged on the substrateand configured to hold charges transferred from at least one of thefirst photoelectric conversion unit, the second photoelectric conversionunit, the third photoelectric conversion unit, and the fourthphotoelectric conversion unit. The first transfer unit is arranged onthe substrate and configured to transfer charges from the firstphotoelectric conversion unit to the first holding portion. The secondtransfer unit is arranged on the substrate and configured to transfercharges from the second photoelectric conversion unit to the firstholding portion. The third transfer unit is arranged on the substrateand configured to transfer charges from the third photoelectricconversion unit to the first holding portion. The fourth transfer unitis arranged on the substrate and configured to transfer charges from thefourth photoelectric conversion unit to the first holding portion. Thefirst amplifier unit includes an input node configured to receivecharges transferred from the first holding portion. The firstphotoelectric conversion unit and the second photoelectric conversionunit are arranged adjacent to each other along a first direction in planview with respect to the substrate. The first photoelectric conversionunit and the third photoelectric conversion unit are arranged adjacentto each other along a second direction, which is different from thefirst direction, in the plan view. The second photoelectric conversionunit and the fourth photoelectric conversion unit are arranged adjacentto each other along the second direction in the plan view. At least apart of the first holding portion is arranged in a region surrounded bythe closest apexes of the first photoelectric conversion unit, thesecond photoelectric conversion unit, the third photoelectric conversionunit, and the fourth photoelectric conversion unit in the plan view.

Further features of the disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a general configuration of aphotoelectric conversion device according to a first embodiment.

FIG. 2 is a block diagram schematically illustrating a configuration ofpixels of two rows by two columns of a pixel array according to thefirst embodiment.

FIG. 3 is an equivalent circuit diagram illustrating a configuration ofa pixel according to the first embodiment.

FIG. 4 is a schematic plan view illustrating an example of a pixellayout according to the first embodiment.

FIG. 5A and FIG. 5B are schematic plan views illustrating an example ofarrangement of control signal lines according to the first embodiment.

FIG. 6A and FIG. 6B are schematic plan views illustrating an example ofa pixel layout and arrangement of control signal lines according to asecond embodiment, respectively.

FIG. 7 is a table illustrating an example of a drive method of a firsttransfer transistor according to the second embodiment.

FIG. 8A and FIG. 8B are schematic plan views illustrating an example ofa pixel layout and arrangement of control signal lines according to athird embodiment, respectively.

FIG. 9 is a table illustrating an example of a drive method of a firsttransfer transistor according to the third embodiment.

FIG. 10 is a schematic plan view illustrating an example of arrangementof color filters according to a fourth embodiment.

FIG. 11 is a block diagram illustrating a configuration example of animaging system according to a fifth embodiment.

FIG. 12A and FIG. 12B are diagrams illustrating a configuration exampleof an imaging system and a moving body according to a sixth embodiment.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the disclosure will now be described in detailin accordance with the accompanying drawings. Note that the samecomponents or corresponding components are labeled with commonreferences throughout multiple drawings, and the description thereof maybe omitted or simplified.

First Embodiment

FIG. 1 is a block diagram illustrating a general configuration of aphotoelectric conversion device according to the present embodiment. Thephotoelectric conversion device may be, for example, an imaging device,a focus detection device, a ranging device, or the like but is notlimited thereto. In the present embodiment, the photoelectric conversiondevice is an imaging device that captures an image such as a staticimage, a moving image, or the like. The photoelectric conversion devicehas a pixel array 110, a vertical scanning circuit 120, a columnamplifier circuit 130, a horizontal scanning circuit 140, an outputcircuit 150, and a control circuit 160. The pixel array 110 has aplurality of pixels 170 arranged so as to form a plurality of rows and aplurality of columns.

The control circuit 160 controls drive timings of each component of thevertical scanning circuit 120, the column amplifier circuit 130, and thehorizontal scanning circuit 140. The vertical scanning circuit 120supplies control signals used for controlling a plurality of transistorsincluded in each pixel 170 to enter an on-state (conductive state) or anoff-state (nonconductive state). The vertical scanning circuit 120 maybe formed of a logic circuit such as a shift register, an addressdecoder, or the like. A column signal line 180 is provided on eachcolumn of the pixel array 110, and signals from the pixels 170 are readout to the column signal lines 180 on a column basis.

The column amplifier circuit 130 performs processes such as anamplification process of signals that have been output to the columnsignal lines 180, a correlated double sampling process based on a signalobtained at reset and a signal obtained at photoelectric conversion inthe pixel 170, or the like. The horizontal scanning circuit 140 suppliescontrol signals used for controlling switches connected to amplifiers ofthe column amplifier circuit 130 to enter the on-state or the off-state.Thereby, the horizontal scanning circuit 140 performs control to outputa signal on a selected column to the output circuit 150. The outputcircuit 150 is formed of a buffer amplifier, a differential amplifier,or the like and outputs a signal from the column amplifier circuit 130to a signal processing unit outside the photoelectric conversion device.Note that the column amplifier circuit 130 may include a function of asignal processing circuit that performs signal processing such ascorrection of a false signal component or the like. An AD convertercircuit may be further provided in the photoelectric conversion device,and thereby the photoelectric conversion device may be configured tooutput digital signals.

FIG. 2 is a block diagram schematically illustrating a configuration ofpixels of two rows and two columns of the pixel array 110 according tothe present embodiment. FIG. 3 is an equivalent circuit diagramillustrating a configuration of a pixel according to the presentembodiment. The configuration of the pixel 170 will be described in moredetail with reference to FIG. 2 and FIG. 3.

FIG. 2 schematically illustrates a configuration of four pixels 170A,170B, 170C, and 170D included in consecutive two rows and two columns ofthe pixel array 110. The pixel 170A is arranged on the first row, thefirst column in FIG. 2. The pixel 170B is arranged on the second row,the first column in FIG. 2. The pixel 170C is arranged on the first row,the second column in FIG. 2. The pixel 170D is arranged on the secondrow, the second column in FIG. 2. In other words, the pixel 170A and thepixel 170B are aligned in the Y direction (first direction), and thepixel 170C and the pixel 170D are also aligned in the Y direction. Thepixel 170A and the pixel 170C are aligned in the X direction (seconddirection), and the pixel 170B and the pixel 170D are also aligned inthe X direction.

The pixel 170A has a first circuit 171A and a second circuit 172A. Thepixel 170B has a first circuit 171B and a second circuit 172B. The pixel170C has a first circuit 171C and a second circuit 172C. The pixel 170Dhas a first circuit 171D and a second circuit 172D.

The second circuit 172A of the pixel 170A is connected not only to thefirst circuit 171A of the pixel 170A but also to the first circuit 171B,the first circuit 171C, and the first circuit 171D of other pixels. Inother words, the second circuit 172A is connected to all the firstcircuits of the four pixels 170A, 170B, 170C, and 170D. Further, thesecond circuit 172A is connected to the column signal line 180 on acorresponding column. This enables addition of signals of pixels onadjacent rows and adjacent columns.

FIG. 3 is an equivalent circuit diagram illustrating a configuration ofthe pixel 170A. Details of the circuit configuration of the pixel 170Awill be described. Note that, since other pixels illustrated in FIG. 2have the same configuration as the pixel 170A, the description thereofwill be omitted.

The pixel 170A has the first circuit 171A and the second circuit 172A.The first circuit 171A has a photoelectric conversion unit PD, fourfirst transfer transistors M1A, M1B, M1C, and M1D, and a dischargingtransistor M2. The second circuit 172A has a charge holding portion MEM,a second transfer transistor M3, a reset transistor M4, an amplifiertransistor M5, and a select transistor M6.

The photoelectric conversion unit PD photoelectrically converts incidentlight and accumulates charges generated by photoelectric conversion. Asthe photoelectric conversion unit PD, a photodiode may be used, forexample. In the following description, the photoelectric conversion unitPD is assumed to be a photodiode having an anode and a cathode. Theanode of the photoelectric conversion unit PD is connected to a groundpotential line, and the cathode is connected to the sources of the firsttransfer transistors M1A, M1B, M1C, and M1D and the source of thedischarging transistor M2. The drain of the first transfer transistorM1A is connected to the source of the second transfer transistor M3. Thecapacitance that is parasitic between the drain of the first transfertransistor M1A and the source of the second transfer transistor M3 formsthe charge holding portion MEM. In other words, the charge holdingportion MEM is connected to the drain of the first transfer transistorM1A. The drain of the discharging transistor M2 is connected to a powersource potential line having a potential VDD.

Further, the charge holding portion MEM of the pixel 170A is alsoconnected to the drain of the first transfer transistor M1D of the pixel170C adjacent in the X direction and the drain of the first transfertransistor M1B of the pixel 170B adjacent in the Y direction.Furthermore, the charge holding portion MEM of the pixel 170A is alsoconnected to the drain of the first transfer transistor M1C of the pixel170D located diagonally of a pixel group of two rows by two columns.

The drain of the second transfer transistor M3 is connected to thesource of the reset transistor M4 and the gate of the amplifiertransistor M5. The connection node of the drain of the second transfertransistor M3, the source of the reset transistor M4, and the gate ofthe amplifier transistor M5 is a floating diffusion region FD. The drainof the reset transistor M4 is connected to the power source potentialline having the potential VDD. The source of the amplifier transistor M5is connected to the drain of the select transistor M6. The drain of theamplifier transistor M5 is connected to the power source potential linehaving the potential VDD. The source of the select transistor M6 isconnected to the column signal line 180. The column signal line 180 isconnected to a current source (not illustrated).

On each row of the pixel array 110, a plurality of control signal lines(not illustrated in FIG. 3) are arranged extending in the X direction.The vertical scanning circuit 120 supplies control signals to the gatesof the plurality of transistors within the pixel 170A via the pluralityof control signal lines.

When the first transfer transistor M1A is controlled to the on-state bya control signal, charges generated and accumulated in the photoelectricconversion unit PD are transferred to the charge holding portion MEM.The charge holding portion MEM holds charges transferred from thephotoelectric conversion unit PD. When the second transfer transistor M3is controlled to the on-state by a control signal, charges held in thecharge holding portion MEM are transferred to the floating diffusionregion PD. Note that, when any one of the first transfer transistorsM1B, M1C, and M1D is controlled to the on-state by a control signal,charges generated and accumulated in the photoelectric conversion unitPD are transferred to the charge holding portion MEM of another pixel.

When the reset transistor M4 is controlled to the on-state by a controlsignal, the potential of the floating diffusion region FD is reset. Whenthe select transistor M6 is controlled to the on-state by a controlsignal, a signal is output from the amplifier transistor M5 on the rowof interest to the column signal line 180. At this time, the amplifiertransistor M5 and the current source connected to the column signal line180 form a source follower circuit that outputs a signal in accordancewith charges transferred to the floating diffusion region FD and therebyfunction as an output unit. Further, at this time, the floatingdiffusion region FD receives charges transferred from the charge holdingportion MEM and thereby functions as an input node of the sourcefollower circuit. When the discharging transistor M2 is controlled tothe on-state by a control signal, charges accumulated in thephotoelectric conversion unit PD are discharged, and the potential ofthe cathode of the photoelectric conversion unit PD is reset.

With the above features, a configuration in which charges are generatedby the photoelectric conversion unit PD and accumulated in thephotoelectric conversion unit PD while charges are held in the chargeholding portion MEM is realized. This enables the photoelectricconversion device to perform driving of a global electronic shutterscheme that matches the start time with the end time of chargeaccumulation in a plurality of photoelectric conversion units PD withinthe pixel array 110. The start of charge accumulation in accordance withthe global electronic shutter scheme can be implemented bysimultaneously controlling a plurality of discharging transistors M2within the pixel array 110 from the on-state to the off-state todischarge charges, for example. Further, the end of charge accumulationin accordance with the global electronic shutter scheme can beimplemented by simultaneously controlling a plurality of first transfertransistors M1A within the pixel array 110 from the off-state to theon-state and then again to the off-state to transfer charges, forexample.

Furthermore, in the configuration of the present embodiment, it ispossible to add signals of pixels on adjacent rows and adjacent columnsby transferring charges from a plurality of photoelectric conversionunit PD to one charge holding portion MEM in addition to performingdriving of a global electronic shutter scheme. Specifically, it ispossible to add signals of pixels on adjacent two rows by controllingthe first transfer transistors M1A of the pixels 170A and 170C and thefirst transfer transistors M1B of the pixels 170B and 170D to theon-state. Further, it is possible to add signals of pixels on adjacenttwo columns by controlling the first transfer transistors M1A of thepixels 170A and 170B and the first transfer transistors M1D of thepixels 170C and 170D to the on-state. In such a way, in the presentembodiment, it is possible to perform driving of column addition or rowaddition to add charges in the charge holding portion MEM (first drivingscheme) by transferring charges from the photoelectric conversion unitsPD of two pixels on adjacent rows or adjacent columns to one chargeholding portion MEM.

Further, it is possible to add signals of four pixels by controlling thefirst transfer transistor M1A of the pixel 170A, the first transfertransistor M1B of the pixel 170B, the first transfer transistor M1D ofthe pixel 170C, and the first transfer transistor M1C of the pixel 170Dto the on-state. In such a way, in the present embodiment, it ispossible to perform driving of 2×2 addition to add charges in the chargeholding portion MEM (second driving scheme) by transferring charges fromthe photoelectric conversion units PD of four pixels on adjacent rowsand columns to one charge holding portion MEM.

Furthermore, by controlling the first transfer transistor M1A of each ofthe pixels 170A, 170B, 170C, and 170D to the on-state, it is possible tooutput a signal without performing addition. In such a way, in thepresent embodiment, by transferring charges from the photoelectricconversion units PD of four pixels to an individual charge holdingportion MEM, it is possible to perform non-addition driving thatperforms no addition (third driving scheme).

Further, it is possible to add signals of three pixels by controllingthe first transfer transistor M1A of the pixel 170A, the first transfertransistor M1B of the pixel 170B, and the first transfer transistor M1Dof the pixel 170C to the on-state. In such a case, the signal from thepixel 170D is output separately from the added signals of three pixels.By outputting an addition signal corresponding to three pixels and anon-addition signal corresponding to one pixel independently of eachother, it is possible to use these signals to perform a High DynamicRange (HDR) process to expand the dynamic range. In such a way, in thepresent embodiment, it is also possible to perform driving to output twotypes of signals used for HDR (fourth driving scheme). Note that, in thesignal output scheme for HDR, it is necessary to be able to output anaddition signal and a non-addition signal, and the number of pixels foran addition signal is not particularly limited. For example, an additionsignal corresponding to two pixels may be output. Further, pixels usedfor an addition signal and a pixel used for a non-addition signal can beset as appropriate out of four pixels and are not particularly limited.As described above, the pixel configuration of the present embodimentcan be adapted to various addition driving and, furthermore, can beadapted to non-addition driving.

Note that, although addition of signals is possible similarly even witha configuration of transferring charges from a plurality of chargeholding portions MEM to one floating diffusion region FD, theconfiguration of adding charges in the charge holding portion MEM of thepresent embodiment is more advantageous for a noise reduction ability.

In the configuration of adding charges in the floating diffusion regionFD, a plurality of transfer transistors are connected to the floatingdiffusion region FD. Since this results in a longer region in which atransfer transistor and the floating diffusion region PD are in contactwith each other, the capacitance of the floating diffusion region FD islarger due to the parasitic capacitance. This increases dark randomnoise. In contrast, in the configuration of adding charges in the chargeholding portion MEM of the present embodiment, since the number oftransfer transistors connected to the floating diffusion region FD isone, the parasitic capacitance is smaller, and dark random noise causedas described above can be reduced. Therefore, in the configuration ofadding charges in the charge holding portion MEM of the presentembodiment, noise can be reduced compared to the configuration of addingcharges in the floating diffusion region FD.

FIG. 4 is a schematic plan view illustrating an example of a pixellayout according to the present embodiment. FIG. 4 illustrates aschematic plan view of four pixels 170A, 170B, 170C, and 170D includedin consecutive two rows and two columns of the pixel array 110. FIG. 4schematically illustrates the photoelectric conversion units PD, thefirst transfer transistors M1A, M1B, M1C, and M1D, the dischargingtransistors M2, the charge holding portions MEM, and the second transfertransistors M3 illustrated in FIG. 3.

Further, FIG. 4 illustrates micro-lenses ML provided in association withthe photoelectric conversion units PD of the pixels 170A, 170B, 170C,and 170D, respectively. Each micro-lens ML is provided such that theoptical axis thereof overlaps the center of the photoelectric conversionunit PD in plan view. In other words, the plurality of micro-lenses MLdefine the optical centers CA, CB, CC, and CD of the photoelectricconversion units PD of the pixels 170A, 170B, 170C, and 170D,respectively.

Further, FIG. 4 illustrates readout circuit units 173. Each readoutcircuit unit 173 includes the reset transistor M4, the amplifiertransistor M5, and the select transistor M6 illustrated in FIG. 3. Thefour readout circuit units 173 illustrated in FIG. 4 (a first amplifierunit, a second amplifier unit, a third amplifier unit, a fourthamplifier unit) are provided so as to correspond to the pixels 170A,170B, 170C, and 170D.

The first transfer transistor M1A of the pixel 170A (first transferunit) is arranged between the photoelectric conversion unit PD of thepixel 170A (first photoelectric conversion unit) and the charge holdingportion MEM of the pixel 170A (first holding portion). The firsttransfer transistor M1B of the pixel 170B (second transfer unit) isarranged between the photoelectric conversion unit PD of the pixel 170B(second photoelectric conversion unit) and the charge holding portionMEM of the pixel 170A. The first transfer transistor M1D of the pixel170C (third transfer unit) is arranged between the photoelectricconversion unit PD of the pixel 170C (third photoelectric conversionunit) and the charge holding portion MEM of the pixel 170A. The firsttransfer transistor M1C of the pixel 170D (sixth transfer unit) isarranged between the photoelectric conversion unit PD of the pixel 170D(fourth photoelectric conversion unit) and the charge holding portionMEM of the pixel 170A. Thereby, charges may be transferred to the chargeholding portion MEM of the pixel 170A from one or two or more of thephotoelectric conversion units PD of the four pixels 170A, 170B, 170C,and 170D. Accordingly, it is possible to output charges generated by aplurality of photoelectric conversion units PD after adding the chargesin the charge holding portion MEM.

Further, the first transfer transistor M1A of the pixel 170B (fourthtransfer unit) is arranged between the photoelectric conversion unit PDof the pixel 170B and the charge holding portion MEM of the pixel 170B(second holding portion). The first transfer transistor M1A of the pixel170C (fifth transfer unit) is arranged between the photoelectricconversion unit PD of the pixel 170C and the charge holding portion MEMof the pixel 170C (third holding portion). The first transfer transistorM1A of the pixel 170D is arranged between the photoelectric conversionunit PD of the pixel 170D and the charge holding portion MEM of thepixel 170D. In such a way, the photoelectric conversion units PD of thepixels 170B, 170C, and 170D can also transfer charges to the chargeholding portions MEM of corresponding pixels. Accordingly, it ispossible to output charges generated by a plurality of photoelectricconversion units PD, respectively, without adding the charges.

Each charge holding portion MEM is arranged at a position that at leastpartially overlaps a straight line connecting the optical center CA tothe optical center CD. Further, each charge holding portion MEM isarranged at a position that at least partially overlaps a straight lineconnecting the optical center CB to the optical center CC. In otherwords, the charge holding portion MEM of the pixel 170A is arranged at aposition that at least partially overlaps a straight line connecting theoptical centers of the diagonally located photoelectric conversion unitsPD of two pixels out of the pixels 170A, 170B, 170C, and 170D on tworows by two columns. The optical center of the photoelectric conversionunit PD can be regarded as the center position of a semiconductor regionformed as a region used for accumulating charges. That is, when chargesto be accumulated are electrons, the optical center of the photoelectricconversion unit PD can be regarded as the center position of an N-typesemiconductor region used for accumulating electrons. Further, fromanother point of view, the optical center of the photoelectricconversion unit PD can be regarded as substantially the center of themicro-lens ML that guides light to the photoelectric conversion unit PD.Note that the center of the micro-lens ML and the center of thephotoelectric conversion unit PD may be shifted from each other as theimage height on an imaging plane increases (that is, as the position ofa pixel is closer to the edge from the center). In such a form, thecenter position of the micro-lens ML of the pixel 170 at the centerposition of the imaging plane (pixel array 110) can be applied to eachof other pixels 170.

Further, from another point of view, at least a part of the chargeholding portion MEM is arranged in a region surrounded by the closestapexes of respective photoelectric conversion units PD of the pixel170A, the pixel 170B, the pixel 170C, and the pixel 170D. The regionsurrounded by the closest apexes (P1, P2, P3, P4) of these fourphotoelectric conversion units PD is denoted as a region G in FIG. 4.The positions of these apexes can be positions of element isolationportions (formed by using various methods such as the STI, DTI, or LOCOSmethod) provided adjacent to the photoelectric conversion units PD, forexample.

Such arrangement of the charge holding portion MEM and the photoelectricconversion units PD increases symmetry of charge transfer paths, anddeterioration of characteristics due to charge transfer paths beingasymmetrical or the like can be reduced. Further, since the chargeholding portion MEM can be arranged at a position away from the opticalcenter of the photoelectric conversion unit PD, noise due to incidentlight entering a part near the charge holding portion MEM can bereduced. Therefore, according to the present embodiment, with thearrangement of the charge holding portion MEM and the photoelectricconversion units PD as described above, a high-performance photoelectricconversion device is provided.

Note that the layout of the photoelectric conversion device may bedesigned such that the upper limit of charges that may be held in thecharge holding portion MEM of the pixel 170A is larger than the upperlimit of charges that may be held in the charge holding portion MEM ofthe pixel 170B, 170C, or 170D. More charges are transferred to thecharge holding portion MEM in which addition of charges is performedthan to the charge holding portion MEM in which addition of charges isnot performed. Thus, by increasing the upper limit of charges that maybe held in the charge holding portion MEM of the pixel 170A in whichaddition of charges is performed, it is possible to expand the dynamicrange.

FIG. 5A and FIG. 5B are schematic plan views illustrating an example ofarrangement of control signal lines according to the present embodiment.FIG. 5A is a diagram illustrating an arrangement example of a controlsignal line group 174 arranged in a first wiring layer located above asemiconductor substrate on which the photoelectric conversion units PDand respective transistors are arranged. FIG. 5B is a diagramillustrating an arrangement example of a control signal line group 175arranged in a second wiring layer located above the first wiring layer.The control signal line groups 174 and 175 include a plurality ofcontrol signal lines extending in the X direction. Since thephotoelectric conversion device of the present embodiment is of afront-illuminated type that receives light from the side on which thefirst wiring layer and the second wiring layer are arranged to thesemiconductor substrate, the control signal line groups 174 and 175 arearranged so as to avoid the photoelectric conversion units PD in planview. However, the present disclosure is also applicable to aback-illuminated type that receives light from the semiconductorsubstrate side. In such a case, it is not essential that the controlsignal line groups 174 and 175 be arranged so as to avoid thephotoelectric conversion units PD in plan view.

The number of control signal lines used for supplying control signals topixels of two rows by two columns illustrated in FIG. 5A and FIG. 5B isat least 23. In the present embodiment, since the first transfertransistors M1A, M1B, M1C, and M1D can be controlled independently ofeach other, the number of control signal lines used for controllingthese first transfer transistors is 16. The number of control signallines provided for the discharging transistor M2 is one, and the numberof control signal lines provided for each of the second transfertransistor M3, the reset transistor M4, and the select transistor M6 istwo.

Second Embodiment

The photoelectric conversion device of the present embodiment isdifferent from the first embodiment in that some of control signals of aplurality of first transfer transistors are used as a common controlsignal to reduce the number of control signal lines. Since the remainingconfigurations are the same as those of the first embodiment, thedescription thereof will be omitted.

FIG. 6A is a schematic plan view illustrating an example of a pixellayout according to the present embodiment. The physical arrangement ofeach component illustrated in FIG. 6A is similar to that in the firstembodiment. FIG. 6B is a diagram illustrating an example of arrangementof the photoelectric conversion unit PD and a control signal line group176 arranged in a first wiring layer located above a semiconductorsubstrate on which respective transistors are arranged. Note that,although an example of arrangement of a second wiring layer is notillustrated in the present embodiment, some of the control signal linesmay also be arranged in the second wiring layer in the same manner as inthe first embodiment.

The blocks illustrating the first transfer transistors M1A, M1B, M1C,and M1D of FIG. 6A are labeled with ten types of references from GS0 toGS9. These references denote control signals to be input to the gates ofrespective transistors. In the first embodiment, since the four firsttransfer transistors M1A, M1B, M1C, and M1D provided in each of the fourpixels can be controlled independently of each other, there are 16 typesof control signals. In contrast, in the present embodiment, since thecommon control signal GS0 is input to some of the transistors, types ofcontrol signals are reduced to ten types. In the present embodiment,since the types of the control signals can be reduced by six typescompared with the first embodiment, the number of required controlsignal lines is reduced from 23 to 17. This can increase the openingarea above the photoelectric conversion unit PD to improve sensitivity.Alternatively, it is possible to employ design to reduce the gap betweenthe photoelectric conversion units PD while securing a sufficientopening area above the photoelectric conversion unit PD, and this canreduce the pixel pitch.

FIG. 7 is a table illustrating an example of a driving method of thefirst transfer transistors M1A, M1B, M1C, and M1D according to thepresent embodiment. FIG. 7 illustrates the levels of control signalscorresponding to respective modes of “non-addition”, “row addition”,“column addition”, “2×2 addition”, and “three-pixel addition”, and typesof signals to be read. Each transistor is turned on when a correspondingcontrol signal is at the high level (HIGH) and is turned off when acorresponding control signal is at the low level (LOW). “A”, “B”, “C”,and “D” in the field “read signal” correspond to signals based oncharges generated by the photoelectric conversion units PD of the pixels170A, 170B, 170C, and 170D, respectively. Further, “A+B” corresponds toan addition signal of the pixel 170A and the pixel 170B. The sameapplies to other denotation.

In the “non-addition” mode, the control signals GS1, GS3, GS7, and GS9are at the high level, and the remaining control signals are at the lowlevel. At this time, the first transfer transistor M1A of each of thepixels 170A, 170B, 170C, and 170D is controlled to be turned on. In sucha case, since charges generated by the photoelectric conversion unit PDof each of the pixels are transferred to different charge holdingportions MEM, no addition is performed, and a signal is output.

In the “row addition” mode, the control signals GS1, GS3, GS4, and GS6are at the high level, and the remaining control signals are at the lowlevel. At this time, the first transfer transistors M1A of the pixels170A and 170B and the first transfer transistors M1D of the pixels 170Cand 170D are controlled to be turned on. In such a case, since chargesgenerated by the photoelectric conversion units PD of pixels on adjacenttwo columns are transferred to the same charge holding portion MEM,signals are added between pixels on the adjacent two columns.

In the “column addition” mode, the control signals GS1, GS2, GS7, andGS8 are at the high level, and the remaining control signals are at thelow level. At this time, the first transfer transistors M1A of pixels170A and 170C and the first transfer transistors M1B of the pixels 170Band 170D are controlled to be turned on. In such a case, since chargesgenerated by the photoelectric conversion units PD of pixels on adjacenttwo rows are transferred to the same charge holding portion MEM, signalsare added between pixels on the adjacent two rows.

In the “2×2 addition” mode, the control signals GS1, GS2, GS4, and GS5are at the high level, and the remaining control signals are at the lowlevel. At this time, the first transfer transistor M1A of the pixel170A, the first transfer transistor M1B of the pixel 170B, the firsttransfer transistor M1D of the pixel 170C, and the first transfertransistor M1C of the pixel 170D are controlled to be turned on. In sucha case, since charges generated by the photoelectric conversion units PDof four pixels on adjacent two rows by two columns are transferred tothe same charge holding portion MEM, signals are added between fourpixels on the adjacent two rows by two columns

In the “three-pixel addition” mode, the control signals GS1, GS2, GS4,and GS8 are at the high level, and the remaining control signals are atthe low level. At this time, the first transfer transistor M1A of thepixel 170A, the first transfer transistor M1B of the pixel 170B, and thefirst transfer transistor M1D of the pixel 170C are controlled to beturned on. Further, the first transfer transistor M1B of the pixel 170Dis controlled to be turned on. In such a case, charges generated by thethree photoelectric conversion units PD of the four pixels on adjacenttwo rows by two columns are transferred to the same charge holdingportion MEM, and signals are added between three pixels. Further,charges generated by the remaining photoelectric conversion unit PD aretransferred to another charge holding portion MEM without being added.By outputting an addition signal for three pixels and a non-additionsignal for a pixel separately, it is possible to perform an HDR processto expand the dynamic range by using these signals.

According to the present embodiment, a high-performance photoelectricconversion device is provided in the same manner as in the firstembodiment. Further, in the present embodiment, it is possible to reducethe number of control signal lines while making it possible to outputsignals corresponding to various addition schemes in the same manner asin the first embodiment and thereby obtain an advantageous effect ofimproved sensitivity or a reduced pixel pitch.

Note that, as illustrated in FIG. 7, the control signal GS0 is always atthe low level in any modes, and a corresponding first transfertransistor is always in the off-state. Therefore, when the off-state ofthe transistor can be implemented, the control signal line used fortransmitting the control signal GS0 may be omitted. Further, the pixelconfiguration may be modified by omitting the first transfer transistorcorresponding to the control signal GS0 so that the photoelectricconversion unit PD and the charge holding portion MEM are insulated fromeach other. Further, the pixel configuration can be modified byemulating a gate electrode of the first transfer transistorcorresponding to the control signal GS0 so that a dummy electrode havingno charge transfer function is arranged near the photoelectricconversion unit PD and the charge holding portion MEM. In theconfiguration in which the first transfer transistor is omitted, sincethe arrangement of electrodes around the photoelectric conversion unitsPD is asymmetric, asymmetricity of the electrodes may affect thephotoelectric conversion characteristic for incident light. In contrast,in the configuration in which the dummy electrode is provided, since thearrangement of the electrode can be symmetric, influence on thecharacteristic due to the first transfer transistor being not providedcan be reduced.

Third Embodiment

The photoelectric conversion device of the present embodiment isdifferent from the second embodiment in that more control signals of aplurality of the first transfer transistors are used as a common controlsignal to further reduce the number of control signal lines. Since theremaining configurations are the same as those of the second embodiment,the description thereof will be omitted.

FIG. 8A is a schematic plan view illustrating an example of a pixellayout according to the present embodiment. The physical arrangement ofeach component illustrated in FIG. 8A is similar to that in the firstembodiment and the second embodiment. FIG. 8B is a diagram illustratingan example of arrangement of the photoelectric conversion unit PD andthe control signal line group 177 arranged in the first wiring layerlocated above the semiconductor substrate on which respectivetransistors are arranged. Note that, although an example of arrangementof the second wiring layer is not illustrated in the present embodiment,some of the control signal lines may also be arranged in the secondwiring layer in the same manner as in the first embodiment.

The blocks illustrating the first transfer transistors M1A, M1B, M1C,and M1D of FIG. 8A are labeled with four types of references from GS0 toGS3. In the present embodiment, the types of control signals are reducedto four types. In the present embodiment, since the types of the controlsignals can be reduced by 12 types compared with the first embodiment,the number of required control signal lines is reduced from 23 to 11.This can increase the opening area above the photoelectric conversionunit PD to improve sensitivity. Alternatively, it is possible to employdesign to reduce the gap between the photoelectric conversion units PDwhile securing a sufficient opening area above the photoelectricconversion unit PD, and this can reduce the pixel pitch.

FIG. 9 is a table illustrating an example of a drive method of the firsttransfer transistors M1A, M1B, M1C, and M1D according to the presentembodiment. In the present embodiment, the types of control signalssupplied to the first transfer transistor connected to the chargeholding portion MEM of the pixel 170A are reduced to two types, andavailable modes are thus limited to the “non-addition” mode and the “2×2addition” mode. Since the specific operation of each mode issubstantially the same as that of the second embodiment, the descriptionthereof will be omitted.

According to the present embodiment, a high-performance photoelectricconversion device is provided in the same manner as in the firstembodiment and the second embodiment. Further, in the presentembodiment, although types of modes are limited compared with the secondembodiment, the number of control signal lines can be further reducedcompared with the configuration of the second embodiment, and therebythe advantageous effect of improved sensitivity or a reduced pixel pitchcan be further enhanced.

Fourth Embodiment

The photoelectric conversion device of the present embodiment has colorfilters in any of the photoelectric conversion devices in the first tothird embodiments. Since the remaining configurations are the same asthose of the first to third embodiments, the description thereof will beomitted.

FIG. 10 is a schematic plan view illustrating an example of arrangementof color filters according to the present embodiment. The photoelectricconversion device of the present embodiment has a color filter aboveeach of the pixels. The color filter has either color of red (R), green(G), or blue (B). Arrangement of colors of the color filters is theBayer Arrangement in which the four pixels 170A, 170B, 170C, and 170D ofthe same color are defined as a unit, as illustrated in FIG. 10. Whenthe color filters corresponding to the photoelectric conversion units PDof the pixels 170A, 170B, 170C, and 170D are defined as a first colorfilter, a second color filter, a third color filter, and a fourth colorfilter, respectively, all the first to fourth color filters have thesame color. That is, all the four pixels 170A, 170B, 170C, and 170Dsubjected to addition have the same color.

With such arrangement, in each of various modes such as the“non-addition” mode or the “2×2 addition” mode, it is possible to causepixel signals of the same color to be added and not to cause pixelsignals of different colors to be added. Therefore, the photoelectricconversion device of the present embodiment can acquire a color image inany mode.

According to the present embodiment, a high-performance photoelectricconversion device is provided in the same manner as in the firstembodiment to the third embodiment. Further, in the present embodiment,the photoelectric conversion device which can acquire a color image isprovided.

Fifth Embodiment

Next, an example of an apparatus to which the photoelectric conversiondevice according to the embodiments described above is applied will bedescribed. FIG. 11 is a block diagram illustrating the configuration ofan imaging system 500 according to the present embodiment. An imagingdevice 10 illustrated in FIG. 11 is any one of the photoelectricconversion device described in the above first to fourth embodiments.The imaging system 500 to which the imaging device 10 is applicable maybe, for example, a digital camera, a digital camcorder, a surveillancecamera, or the like. FIG. 11 illustrates a configuration example of adigital camera to which the imaging device 10, which is an example ofthe photoelectric conversion device described in the above embodiments,is applied.

The imaging system 500 illustrated as an example in FIG. 11 has theimaging device 10, a lens 502 that captures an optical image of asubject onto the imaging device 10, an aperture 504 for changing a lightamount passing through the lens 502, and a barrier 506 for protectingthe lens 502. The lens 502 and the aperture 504 form an optical systemthat collects a light onto the imaging device 10.

The imaging system 500 further has a signal processing unit 508 thatprocesses an output signal output from the imaging device 10. The signalprocessing unit 508 performs a signal processing operation to performvarious correction or compression on the input signal if necessary andoutput the processed input signal.

The imaging system 500 further has a buffer memory unit 510 used fortemporarily storing image data therein and an external interface unit(external I/F unit) 512 used for communicating with an external computeror the like. The imaging system 500 further has a storage medium 514such as a semiconductor memory used for performing storage or readout ofimaging data and a storage medium control interface unit (storage mediumcontrol I/F unit) 516 used for performing storage or readout on thestorage medium 514. Note that the storage medium 514 may be embedded inthe imaging system 500 or may be removable.

Furthermore, the imaging system 500 has a general control/operation unit518 that performs various calculation and controls the overall digitalcamera and a timing generation unit 520 that outputs various timingsignals to the imaging device 10 and the signal processing unit 508.Herein, the timing signal or the like may be externally input, and theimaging system 500 may have at least the imaging device 10 and thesignal processing unit 508 that processes an output signal output fromthe imaging device 10. The general control/operation unit 518 and thetiming generation unit 520 may be configured to perform a part or all ofthe function related to control of the photoelectric conversion device,such as generation of a control signal, generation of a referencevoltage, or the like in the embodiments described above.

The imaging device 10 outputs an image signal to the signal processingunit 508. The signal processing unit 508 performs predetermined signalprocessing on an image signal output from the imaging device 10 andoutputs image data. Further, the signal processing unit 508 uses animage signal to generate an image.

As described above, the imaging system 500 of the present embodimentincludes the imaging device 10 according to any of the first to fourthembodiments. Accordingly, the imaging system 500 that enables a higherquality image capturing can be realized.

Sixth Embodiment

FIG. 12A and FIG. 12B are diagrams illustrating a configuration of animaging system 600 and a moving body according to the presentembodiment. FIG. 12A illustrates an example of an imaging system 600related to an on-vehicle camera. An imaging system 600 has an imagingdevice 10 that is an example of the photoelectric conversion devicedescribed in any of the above first to fourth embodiments. The imagingsystem 600 has an image processing unit 612 that performs imageprocessing on a plurality of image data acquired by the imaging device10 and a parallax calculation unit 614 that calculates a parallax (aphase difference of parallax images) from the plurality of image dataacquired by the imaging system 600. Further, the imaging system 600 hasa distance measurement unit 616 that calculates a distance to the objectbased on the calculated parallax and a collision determination unit 618that determines whether or not there is a collision possibility based onthe calculated distance. Herein, the parallax calculation unit 614 andthe distance measurement unit 616 are an example of a distanceinformation acquisition unit that acquires distance information on thedistance to the object. That is, the distance information is informationon a parallax, a defocus amount, a distance to an object, or the like.The collision determination unit 618 may use any of the distanceinformation to determine the collision possibility. The distanceinformation acquisition unit may be implemented by dedicatedly designedhardware or may be implemented by a software module. Further, thedistance information acquisition unit may be implemented by a fieldprogrammable gate array (FPGA), an application specific integratedcircuit (ASIC), or the like or may be implemented by a combinationthereof.

The imaging system 600 is connected to the vehicle informationacquisition device 620 and can acquire vehicle information such as avehicle speed, a yaw rate, a steering angle, or the like. Further, theimaging system 600 is connected to a control ECU 630, which is a controldevice that outputs a control signal for causing a vehicle to generatebraking force based on a determination result by the collisiondetermination unit 618. That is, the control ECU 630 is an example of amoving body control unit that controls a moving body based on distanceinformation. Further, the imaging system 600 is also connected to analert device 640 that issues an alert to the driver based on adetermination result by the collision determination unit 618. Forexample, when the collision probability is high as the determinationresult of the collision determination unit 618, the control ECU 630performs vehicle control to avoid a collision or reduce damage byapplying a brake, pushing back an accelerator, suppressing engine power,or the like. The alert device 640 alerts a user by sounding an alertsuch as a sound, displaying alert information on a display of a carnavigation system or the like, providing vibration to a seat belt or asteering wheel, or the like.

In the present embodiment, an area around a vehicle, for example, afront area or a rear area is captured by using the imaging system 600.FIG. 12B illustrates the configuration of the imaging system 600 when afront area of a vehicle (a capturing area 650) is captured. The vehicleinformation acquisition device 620 transmits an instruction to cause theimaging system 600 to operate and perform image capturing. The imagingsystem 600 of the present embodiment including the imaging device 10according to the first to fourth embodiments can further improve theranging accuracy.

Although the example of control for avoiding a collision to anothervehicle has been described above, the embodiment is applicable toautomatic driving control for following another vehicle, automaticdriving control for not going out of a traffic lane, or the like.Furthermore, the imaging system is not limited to a vehicle such as thesubject vehicle and can be applied to a moving body (moving apparatus)such as a ship, an airplane, or an industrial robot, for example. Inaddition, the imaging system can be widely applied to a device whichutilizes object recognition, such as an intelligent transportationsystem (ITS), without being limited to moving bodies.

Other Embodiments

Note that each of the embodiments described above merely illustrates anembodied example in implementing the disclosure, and the technical scopeof the disclosure is not to be construed in a limiting sense by theseembodiments. That is, the disclosure can be implemented in various formswithout departing from the technical concept or the primary featurethereof. For example, it should be understood that an embodiment inwhich a part of the configuration of any of the embodiments is added toanother embodiment or an embodiment in which a part of the configurationof any of the embodiments is replaced with a part of the configurationof another embodiment is also one of the embodiments to which thedisclosure may be applied.

Further, although it is assumed in the description of the aboveembodiments that the scheme of electronic shutter used for driving thephotoelectric conversion device is a global electronic shutter scheme,the scheme is not limited thereto and may be, for example, a rollingshutter scheme.

Further, although the layout, a drive method, or the like have beendescribed for four pixels of two rows by two columns in the illustrationof the above embodiments, this is a mere example, and the number ofadded pixels can be changed as appropriate. To realize both addition ofsignals of two rows and addition of signals of two columns, the numberof added pixels is at least three. Further, the number of added pixelsmay be five or greater.

Embodiments of the disclosure can also be realized by a computer of asystem or apparatus that reads out and executes computer executableinstructions (e.g., one or more programs) recorded on a storage medium(which may also be referred to more fully as a ‘non-transitorycomputer-readable storage medium’) to perform the functions of one ormore of the above-described embodiments and/or that includes one or morecircuits (e.g., application specific integrated circuit (ASIC)) forperforming the functions of one or more of the above-describedembodiments, and by a method performed by the computer of the system orapparatus by, for example, reading out and executing the computerexecutable instructions from the storage medium to perform the functionsof one or more of the above-described embodiments and/or controlling theone or more circuits to perform the functions of one or more of theabove-described embodiments. The computer may comprise one or moreprocessors (e.g., central processing unit (CPU), micro processing unit(MPU)) and may include a network of separate computers or separateprocessors to read out and execute the computer executable instructions.The computer executable instructions may be provided to the computer,for example, from a network or the storage medium. The storage mediummay include, for example, one or more of a hard disk, a random-accessmemory (RAM), a read only memory (ROM), a storage of distributedcomputing systems, an optical disk (such as a compact disc (CD), digitalversatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, amemory card, and the like.

While the disclosure has been described with reference to exemplaryembodiments, it is to be understood that the disclosure is not limitedto the disclosed exemplary embodiments. The scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2019-199911, filed Nov. 1, 2019, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A photoelectric conversion device comprising: asubstrate; a first photoelectric conversion unit, a second photoelectricconversion unit, and a third photoelectric conversion unit that arearranged on the substrate and each configured to generate charges inaccordance with incident light; a first holding portion arranged on thesubstrate and configured to hold charges transferred from at least oneof the first photoelectric conversion unit, the second photoelectricconversion unit, and the third photoelectric conversion unit; a firsttransfer unit arranged on the substrate and configured to transfercharges from the first photoelectric conversion unit to the firstholding portion; a second transfer unit arranged on the substrate andconfigured to transfer charges from the second photoelectric conversionunit to the first holding portion; a third transfer unit arranged on thesubstrate and configured to transfer charges from the thirdphotoelectric conversion unit to the first holding portion; and a firstamplifier unit including an input node configured to receive chargestransferred from the first holding portion; wherein the firstphotoelectric conversion unit and the second photoelectric conversionunit are arranged adjacent to each other along a first direction in planview with respect to the substrate, wherein the first photoelectricconversion unit and the third photoelectric conversion unit are arrangedadjacent to each other along a second direction, which is different fromthe first direction, in the plan view, and wherein the first holdingportion is arranged at a position at least partially overlapping astraight line connecting an optical center of the second photoelectricconversion unit to an optical center of the third photoelectricconversion unit in the plan view.
 2. The photoelectric conversion deviceaccording to claim 1, wherein the photoelectric conversion device isconfigured to be driven by a first drive scheme in which each of thefirst transfer unit and the second transfer unit transfers charges tothe first holding portion to cause charges generated by the firstphotoelectric conversion unit and the second photoelectric conversionunit to be added in the first holding portion.
 3. The photoelectricconversion device according to claim 1, wherein the photoelectricconversion device is configured to be driven by a second drive scheme inwhich each of the first transfer unit, the second transfer unit, and thethird transfer unit transfers charges to the first holding portion tocause charges generated by the first photoelectric conversion unit, thesecond photoelectric conversion unit, and the third photoelectricconversion unit to be added in the first holding portion.
 4. Thephotoelectric conversion device according to claim 1 further comprising:a second holding portion and a third holding portion that are arrangedon the substrate and configured to hold charges; a fourth transfer unitthat is arranged on the substrate and configured to transfer chargesfrom the second photoelectric conversion unit to the second holdingportion; a fifth transfer unit that is arranged on the substrate andconfigured to transfer charges from the third photoelectric conversionunit to the third holding portion; a second amplifier unit including aninput node configured to receive charges transferred from the secondholding portion; and a third amplifier unit including an input nodeconfigured to receive charges transferred from the third holdingportion.
 5. The photoelectric conversion device according to claim 4,wherein the photoelectric conversion device is configured to be drivenby a third drive scheme in which the first transfer unit transferscharges generated by the first photoelectric conversion unit to thefirst holding portion, the fourth transfer unit transfers chargesgenerated by the second photoelectric conversion unit to the secondholding portion, and the fifth transfer unit transfers charges generatedby the third photoelectric conversion unit to the third holding portion.6. The photoelectric conversion device according to claim 4, wherein thephotoelectric conversion device is configured to be driven by a fourthdrive scheme in which the first transfer unit and the second transferunit transfer charges to the first holding portion to cause chargesgenerated by the first photoelectric conversion unit and the secondphotoelectric conversion unit to be added in the first holding portionand the fifth transfer unit transfers charges to the third holdingportion.
 7. The photoelectric conversion device according to claim 4,wherein an upper limit to which charges are held in the first holdingportion is larger than an upper limit to which charges are held in thesecond holding portion or the third holding portion.
 8. Thephotoelectric conversion device according to claim 1 further comprisinga dummy electrode that is arranged near at least one of the firstphotoelectric conversion unit, the second photoelectric conversion unit,and the third photoelectric conversion unit and configured to have nofunction of transferring charges.
 9. The photoelectric conversion deviceaccording to claim 1 further comprising: a first color filter arrangedin association with the first photoelectric conversion unit; a secondcolor filter arranged in association with the second photoelectricconversion unit; and a third color filter arranged in association withthe third photoelectric conversion unit, wherein the first color filter,the second color filter, and the third color filter have the same color.10. The photoelectric conversion device according to claim 1, whereinthe first transfer unit, the second transfer unit, and the thirdtransfer unit operate based on control signals that are different fromeach other.
 11. The photoelectric conversion device according to claim1, wherein the second transfer unit and the third transfer unit operatebased on a common control signal.
 12. The photoelectric conversiondevice according to claim 1 further comprising a micro-lens that guideslight to one of the first photoelectric conversion unit, the secondphotoelectric conversion unit, and the third photoelectric conversionunit, wherein the optical center is the center of the micro-lens. 13.The photoelectric conversion device according to claim 1 furthercomprising: a fourth photoelectric conversion unit that is arranged onthe substrate and configured to generate charges in accordance withincident light; and a sixth transfer unit that is arranged on thesubstrate and configured to transfer charges from the fourthphotoelectric conversion unit to the first holding portion, wherein thethird photoelectric conversion unit and the fourth photoelectricconversion unit are arranged adjacent to each other along the firstdirection in the plan view, and wherein the second photoelectricconversion unit and the fourth photoelectric conversion unit arearranged adjacent to each other along the second direction in the planview.
 14. A photoelectric conversion device comprising: a substrate; afirst photoelectric conversion unit, a second photoelectric conversionunit, a third photoelectric conversion unit, and a fourth photoelectricconversion unit that are arranged on the substrate and each configuredto generate charges in accordance with incident light; a first holdingportion that is arranged on the substrate and configured to hold chargestransferred from at least one of the first photoelectric conversionunit, the second photoelectric conversion unit, the third photoelectricconversion unit, and the fourth photoelectric conversion unit; a firsttransfer unit arranged on the substrate and configured to transfercharges from the first photoelectric conversion unit to the firstholding portion; a second transfer unit arranged on the substrate andconfigured to transfer charges from the second photoelectric conversionunit to the first holding portion; a third transfer unit arranged on thesubstrate and configured to transfer charges from the thirdphotoelectric conversion unit to the first holding portion; a fourthtransfer unit arranged on the substrate and configured to transfercharges from the fourth photoelectric conversion unit to the firstholding portion; and a first amplifier unit including an input nodeconfigured to receive charges transferred from the first holdingportion; wherein the first photoelectric conversion unit and the secondphotoelectric conversion unit are arranged adjacent to each other alonga first direction in plan view with respect to the substrate, whereinthe first photoelectric conversion unit and the third photoelectricconversion unit are arranged adjacent to each other along a seconddirection, which is different from the first direction, in the planview, wherein the second photoelectric conversion unit and the fourthphotoelectric conversion unit are arranged adjacent to each other alongthe second direction in the plan view, and wherein at least a part ofthe first holding portion is arranged in a region surrounded by theclosest apexes of the first photoelectric conversion unit, the secondphotoelectric conversion unit, the third photoelectric conversion unit,and the fourth photoelectric conversion unit in the plan view.
 15. Thephotoelectric conversion device according to claim 13, wherein the firstholding portion is arranged at a position at least partially overlappinga straight line connecting an optical center of the first photoelectricconversion unit to an optical center of the fourth photoelectricconversion unit in the plan view.
 16. The photoelectric conversiondevice according to claim 14, wherein the first holding portion isarranged at a position at least partially overlapping a straight lineconnecting an optical center of the first photoelectric conversion unitto an optical center of the fourth photoelectric conversion unit in theplan view.
 17. An imaging system comprising: the photoelectricconversion device according to claim 1; and a signal processing unitconfigured to process a signal output from the photoelectric conversiondevice.
 18. An imaging system comprising: the photoelectric conversiondevice according to claim 14; and a signal processing unit configured toprocess a signal output from the photoelectric conversion device.
 19. Amoving body comprising: the photoelectric conversion device according toclaim 1; a distance information acquisition unit configured to acquiredistance information on a distance to an object, from a parallax imagebased on signals from the photoelectric conversion device; and a controlunit configured to control the moving body based on the distanceinformation.
 20. A moving body comprising: the photoelectric conversiondevice according to claim 14; a distance information acquisition unitconfigured to acquire distance information on a distance to an object,from a parallax image based on signals from the photoelectric conversiondevice; and a control unit configured to control the moving body basedon the distance information.